The invention relates to an apparatus for cutting plastic profiles with a knife which is guided transversally to the profile and comprises a cutting section having a blade and a holding section, with the cutting section extending substantially parallel to the blade and having a larger thickness than the holding section.
Hollow-chamber profiles are extruded into a continuous strand in profile extrusion from materials that can be plastified such as PVC for example and cut to a defined length of e.g. 6,000 mm into profile bars by means of a trimming apparatus. Special sawing units (e.g. flying circular saws) are mainly used for cutting the profiles into length. Due to numerous disadvantages such as the occurrence of dust, production of chips and high levels of noise, alternative methods are increasingly gaining in importance.
Trimming apparatuses for the virtually noiseless severing of profiles made of plastic, and preferably hollow-chamber profiles made of thermoplastic materials, have long been known and are increasingly used in plastic profile extrusion. The principle is based on the known technology of severing by means of a thin plate which is moved in a somewhat even manner through the profile to be severed. This knife plate is provided with a sharp blade. During the contact with the plastic profile a high local cutting pressure is obtained at the blade edge, which pressure produces a molecular transformation in the plastic matrix. A minimal portion of time is needed for the process of molecular transformation, which is why the severing cannot occur abruptly, but requires the adherence to a certain material-dependent minimum speed. A severing knife that is guided in an abrupt manner through the profile would lead to a cutting process similar to a brittle fracture, characterized by splinterings, large deformations and a cutting surface progress that departs from an even surface.
The breakthrough on the market is still obstructed by deficiencies which are linked to this technology. These deficiencies include, among other things, the partly marked deformations of the profile ends in the area of the severing plane which shows more or less strong divergences of the profile walls in the zone of the severing surface due to material crowding by the thickness of the knife plate and the progress of the cutting surface which diverges from the plane surface. Even if the production of profile bars concerns the production of semi-finished goods, special requirements are placed on the quality of the ends of the profile bars, not the least because the geometrical quality of the profile bars is determined by the cross section of the profile bar ends. In the case of an automated check of the profile geometry the performance of a quality check must be possible without any additionally necessary machining of the ends.